Field of the Invention
The present invention relates to an epitaxial growth apparatus, and particularly to an epitaxial growth apparatus having a heating structure used to efficiently and evenly heat a wafer in a chamber.
Description of Related Art
An epitaxial growth apparatus is widely used as an apparatus for forming a single crystal layer (epitaxial layer) on the surface of a silicon wafer, for example. In a single wafer-type epitaxial growth apparatus, while a source gas is introduced into a camber in which one wafer is placed horizontally, heating is carried out to achieve a predetermined temperature, thereby growing an epitaxial layer.
The wafer needs to be heated at a high temperature ranging from 1,000 to 1,200 degrees Celsius. Halogen lamps are used as the heating source. Many halogen lamps are arranged in an upper and a lower portion of the chamber. In the upper portion of the chamber, a pyrometer is provided to measure the surface temperature of the wafer. The pyrometer is designed to measure the temperature by receiving thermal radiation energy from an object to be measured. Therefore, an obstacle or an opaque must not exist between the pyrometer and the object to be measured. This is why the halogen lamps are usually arranged in a ring around the pyrometer so as not to be an obstacle between the pyrometer and the wafer.
In order to make the epitaxial layer on the wafer plane as uniform in thickness as possible, the temperature distribution within the wafer plane that is heated by the halogen lamps needs to be as uniform as possible. In the case of Japanese Patent Application Laid-Open No. 2000-138170, a substantially cylindrical reflection member is placed inside the ring of halogen lamps. The reflection member is shaped in such a way that a lower end position of a portion corresponding to each outer heating halogen lamp is lower than a lower end position of a portion corresponding to each inner heating halogen lamp. Infrared rays that are supposed to travel to the inner side of the wafer from each outer heating halogen lamp are reflected by the reflection member before traveling to the outer side of the wafer. Therefore, the amount of infrared rays emitted to a central portion of the wafer is reduced.
Japanese Patent Application Laid-Open No. 2011-146537 discloses an epitaxial production apparatus with a structure in which a lower end portion of a substantially cylindrical reflection wall provided on an outer side of an upper lamp group is tilted to an inner side. In this structure, electromagnetic waves that are radiated in the vertically downward direction from any heating lamp of the upper lamp group are guided to an end portion of the wafer after being reflected by the tilted surface. Therefore, this structure can prevent silicon from adhering to an end portion of the back surface of the wafer, and therefore makes it possible to improve the flatness of the wafer.
However, according to the configuration of the conventional epitaxial growth apparatus, the temperature distribution within the wafer plane heated by the halogen lamps is not sufficiently uniform due to the effects of the reflection member. Therefore, the epitaxial layer may be uneven in thickness. Particularly in the case where the halogen lamps are separated into the outer heating group and the inner heating group as disclosed in Japanese Patent Application Laid-Open No. 2000-138170 and the reflection member is provided in the upper portion of the chamber, the temperatures in the central and outer peripheral regions of the wafer tend to be high, while the intermediate region between the central and outer peripheral regions tends to be low.
If the substantially cylindrical reflection member is provided above the wafer, a flow of air flowing from the upper side to the lower side via the inner portion of the reflection member is generated, and this air flow directly hits a central portion of an upper dome of the chamber that covers the space above the wafer. Therefore, the temperature of the central portion of the upper dome tends to drop, and the problem is that by-products of silicon can easily adhere to the upper dome. If the by-products are attached, the thermal radiation energy from the halogen lamps cannot easily pass through the upper dome. As a result, the temperature in the central region of the wafer is more likely to drop, and the temperature distribution within the wafer plane becomes even more uneven.